1. Field of the Invention
Our present invention relates to a drafting frame for a spinning machine, and, more particularly, to a drafting frame having a pneumatic compactor for the sliver or roving.
2. Background of the Invention
A spinning machine is usually provided with a drafting frame having upper and lower rollers and through which the sliver or roving passes, the upper rollers being weighted against the sliver. The lower rollers may extend over numerous sliver paths, each of which delivers the sliver to a respective spindle of the spinning machine while the upper roller may be limited to the respective paths and it is not uncommon for each weighting arm to carry the upper drafting rollers for two such paths or spindles.
It is known to provide a pneumatic compacting device for each drafting path of such a drafting frame (see DE 198 15 325) by disposing between the drafting frame and the wind-up device with its twist-defining location, a perforated compaction element below a shield. Suction is applied to the row of perforations on this element to draw the fibers of the roving inwardly toward the roving center and thereby compact the roving before it receives a twist and is wound on a bobbin.
In this construction, the output lower roller of the drafting frame may be formed as a perforated roller and the shield with which it is juxtaposed lies above the perforated roller and has an air-guiding function so that the incoming air, drawn out through the suction opening acts from both sides of the sliver and thereby improves the yarn quality. The spacing of the shield from the lower suction roller must be adjusted at each spinning station individually and, since the shield is provided on the weighting arm, generally the mobility of the weighting arm must be also controlled. These requirements contribute to a time-consuming setup of the apparatus, require frequent readjustments and create conditions whereby, if careful adjustments are not made, the quality of the yarn may be adversely affected.
It is the principal object of the present invention to provide a drafting frame with a pneumatic compactor, i.e. a device which tends to draw, by suction, fibers of a sliver inwardly toward the center thereof, whereby drawbacks of earlier systems are avoided.
Another object of this invention is to provide a drafting frame for a spinning machine in which the need for adjustment and resetting of parts of the pneumatic compaction unit are minimized, wherein the energy consumption for generating the suction is optimized and the servicing of the drafting frame is facilitated.
Another object of this invention is to optimize the suction air flow in a sliver compactor for a drafting frame of a spinning machine.
These objects and others which will become apparent hereinafter are attained, in accordance with the present invention by providing the shield element as a continuous elongated profile or shield segment extending over a multiplicity of spinning stations below the drafting field plane and mounted on the machine frame. Of course, the shield itself can be one of a plurality of aligned segments as long as each segment extends over a multiplicity of spinning stations, i.e. at least four and all are mounted on the machine frame below the perforated element. Each shield element or segment can thus extend over 4, 6, 8, 10 or 12 spinning stations and hence sliver paths, each of which can be provided with its own perforated member to which suction is applied on the side thereof opposite that at which the perforated member engages the sliver. The perforated member is usually a belt but can be a roller and the suction hood communicating with the perforations along the periphery of the member can extend over at least the width of the shield element. According to a feature of the invention, the shield element is of continuous elongated profile of uniform cross section, i.e. a structural shape, with a T or V shaped cross section or can be of a polygonal cross section and is advantageously mounted below the stitching field plane. This system permits the shield element to cover large areas without restricting the servicing of the drafting frame.
The ends of the profile can be received in rails or frame members forming supports for the drafting frame and particularly at the bearings and the lower rollers of the drafting frame. The bearing mounts can be provided with recesses in which the profile members or shields can be seated from above so that absolutely no adjustment of the shield elements is required. Their positions can be fixed for all spinning stations in each section of the machine over which the particular shield segment extends.
According to another feature of the invention the surface of the shield juxtaposed with the surface formed with the suction opening or openings can conform to the contour of the transport surface, i.e. the surface along which the sliver is entrained. In the case of a convex contour of the transport surface, the juxtaposed surface of the shield will be concave, for example.
According to another aspect of the invention, the shield can be mounted directly on the suction device.
The shield element can be provided with a resilient tongue which can retain the shield in a closed position and can at least partly close the space in which the sliver is guided and which is defined between the shield and the transport surface with its perforation. For ease in threading the sliver into this space, the tongue can be pressed downwardly to allow the sliver to be inserted. The fact that the shield can be deflected can also facilitate replacement of the transport surface, e.g. a perforated belt. Since the shield element is elastic, it can be opened by pressure of the sliver or yarn thereof when, for example, the tension is applied to the strand and can then close automatically after the strand has been inserted or removed. The spring system can be the intrinsic elasticity of the large-area shielding element itself.
In both constructions in accordance with the invention, the suction flow around the yarn can be optimized by the air guiding characteristics of the large-area shield element and the energy requirements for generating the suction can be reduced. The serviceability of the drafting frame, especially in threading the sliver through the frame at the start-up of spinning and in cleaning of the drafting frame, is not hindered by the system of the invention.
The drafting frame according to the first aspect of the invention thus comprises:
a drafting zone comprising a roller support, and a plurality of roller pairs successively traversed by respective slivers for delivery to respective spinning stations whereby each sliver is drafted in a drafting field plane between successive roller pairs, the drafting zone having at least one output roller;
a feed unit on the support spaced from the output roller and supplying each sliver to the respective spinning station;
a transporter between the output roller and the feed unit and formed with a moving transport surface having at least one perforation assigned to each sliver and traveling across a suction opening applying suction to the respective sliver to compact the sliver; and
an elongated shielding element juxtaposed with the surface over an effective region of the suction opening and extending longitudinally over a plurality of spinning stations while being affixed to the support below the drafting field plane.
In accordance with a second aspect of the invention the drafting frame can comprise:
a drafting zone comprising a roller support, and a plurality of roller pairs successively traversed by respective slivers for delivery to respective spinning stations whereby each sliver is drafted in a drafting field plane between successive roller pairs, the drafting zone having at least one output roller;
a feed unit on the support spaced from the output roller and supplying each sliver to the respective spinning station;
a suction unit forming a sliver compactor between the output roller and the feed unit and comprising a moving transport surface having at least one perforation assigned to each sliver and traveling across a suction opening applying suction to the respective sliver to compact the sliver; and
a large-area shielding element juxtaposed with the surface and affixed directly to the suction unit.